Since it is necessary to precisely control the quantity of developing toner in order to obtain an excellent image, it is indispensable to sufficiently stabilize a charge amount of toner relative to changes in ambient conditions and to the lapse of time. Therefore, a charge controlling agent CCA is generally incorporated into a developing agent together with a binder resin and a coloring agent.
For example, a low molecular weight substance having a structure of a quaternary ammonium salt, organophosphorus or phosphate compound is employed for a positively electrifiable toner, whereas a low molecular weight substance having a structure of metal salt of salicylic acid or a structure of tetraphenyl borate is employed for a negatively electrifiable toner. Alternatively, it is also possible to improve the charging characteristics of a developing agent by providing a binder resin to be employed with a charge controlling capability. For this purpose, there has been practiced the introduction of a polar group into a binder resin or to incorporate a resin having a polar group into a developing agent.
In the introduction of a polar group into a binder resin, the method that has been conventionally practiced is to modify the binder resin with guanamine or a guanamine derivative by taking advantage of the terminal OH group of polyester; to allow the primary amine of epoxy resin to react with dihydric phenols; to allow the epoxy group of epoxy resin to react with alcohols, etc.; to seal the terminal OH group and acid group of polyester using a masking agent; or to allow the epoxy group of epoxy resin to react with a monovalent active hydrogen-containing compound.
In the incorporation of a resin having a polar group to a binder resin, the resins that have been employed as a resin having a polar group are a copolymer of an amino group-containing compound, a polysilane compound, a copolymer of styrene with a quaternary ammonium salt, etc.
Further, it is known that the charge amount of a developing agent is influenced by the ambient atmosphere, i.e. the charge amount of a developing agent increases under the conditions of low temperature and low humidity, but decreases under the conditions of high temperature and high humidity. Namely, under the conditions of high temperature and high humidity, water molecules are assumed to adsorb onto the toner, which dissipates the electric charge from the toner. Accordingly, there have been taken various countermeasures such as the incorporation of a charge controlling agent as mentioned above, and the surface treatment of toner using a substance exhibiting hydrophobicity. However, it is still impossible, with these conventional countermeasures, to sufficiently control the charge amount of a developing agent, thus raising a problem that an image exhibiting prominent blushing would be produced under the conditions of high temperature and high humidity.
This invention has been accomplished in view of the aforementioned circumstances, and therefore, an object of this invention is to provide an image forming apparatus which is capable of suppressing fluctuations in the charge amount due to changes in ambient conditions and to the lapse of time, and therefore capable of stably obtaining an image of excellent quality.
According to a first aspect of this invention, there is provided an image forming apparatus comprising;
an image carrier;
a developing device for visualizing an electrostatic latent image formed on the image carrier by a developing agent to form a developing agent image, the developing device being disposed to face the image carrier and provided with a member containing a photocatalytic component which is capable of photo-decomposing water molecules to thereby produce active oxygen, and with a light-irradiating mechanism for irradiating light with a wavelength for activating the photocatalytic component;
a transferring device for transferring the developing agent image onto a recording material; and
a fixing device for fixing the transferred developing agent image onto the recording material.
According to a second aspect of this invention, there is provided a developing agent comprising a binder resin, a coloring agent, and a photocatalytic component which is capable of photo-decomposing water molecules to thereby produce active oxygen.
The developing agent according to this invention is suited for use in the image forming apparatus of this invention.
According to the present invention, it is now possible to decompose water molecules in the atmosphere inside the developing device, in particular, water components, etc., which are adsorbed onto the developing agent by the photocatalytic effect. As a result, it is now possible to prevent the dissipation of electric charge of a developing agent resulting from the water that has been adsorbed onto the developing agent. As explained above, it is possible, through the employment of this invention, to suppress fluctuations in charge amount due to changes in ambient conditions and to the lapse of time, thereby making it possible to stably obtain an image of excellent quality.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.